The proposed studies represent an extension of our efforts to reveal the basic arrangements of neurons and their synapses in cerebral cortex. This knowledge is fundamental to being able to understand the neuronal circuits that underlie the physiological responses of cortical neurons. We have been able to demonstrate for the first time that the pyramidal neurons in rat, cat and macaque visual cortex are organized into vertical oriented, multineuronal units that are centered around clusters of apical dendrites and extend through the depth of the cortex. The next questions to be asked are whether similar modules of pyramidal cells exist in other cortical areas, and whether the GABAergic, inhibitory neurons are arranged in systematic patterns relative to the pyramidal cell modules. If the pyramidal and nonpyramidal cells are arranged to form basic multineuronal units that are similar in all neocortical areas, then it is possible that cortical areas all process afferent information in a similar manner, as is suggested by recent experiments by others on the manipulation of thalamic inputs. To pursue this proposition, it is intended to examine and compare the neuronal patterns in a number of selected cortical areas in rat and monkey. Related to this, it is proposed to make a more complete examination of macaque striate cortex. This cortical area is unique in a number of ways, and in it we have found sets of interrelated neuronal patterns, which need to be examined in more detail. The last part of the proposal is concerned with the synaptic input to cortical neurons, a subject about which there is very little information. We have recently shown that in rat visual cortex it is possible to distinguish between the axons terminals originating from different kinds of nonpyramidal cells. This makes it possible for the first time to compare the inputs of cortical neurons. It is proposed therefore, to compare the axosomatic inputs of various types of pyramidal cells which have different response properties, to determine if the responses can be correlated with the inhibitory inputs to the soma of the neurons. Taken together these studies will significantly expand our knowledge of neuronal organization in cerebral cortex. If regularly repeating neuronal and synaptic patterns are revealed, there will be a strong suggestion that the functioning of the cortex should not be interpreted on the basis of individual neurons, but on the basis of fundamental neuronal circuits that are common to all cortical areas.